Magnetic compasses have been extremely useful for sensing directions and have been used for assistance in navigation over centuries. A pocket compass is a familiar personal item, with its suspended magnetized needle pointing to the magnetic North pole. Some cars are outfitted with a magnetic dial rotatably suspended in a transparent liquid-filled plastic enclosure mounted on the windshield or dashboard. In recent years with the advent of MEMS e-compass (micro-electromechanical system electronic compass) technology it is now possible to achieve convenient, low-cost electronic compassing in consumer and commercial portable applications. MEMS based accelerometers and e-compasses are low cost feasible options to provide navigation assistance to GPS for short durations.
Inertial navigation system (INS) technology has been based on gyroscope and accelerometers. For example, accelerometers can be assembled together with three perpendicular-mounted gyroscopes pivoted on gimbals and have provided in inertial platform that maintains pre-established directions of accelerometer sensor axes no matter how a vehicle moves, rotates, or generally changes direction of motion due to yaw, pitch and roll. E-compass has a miniature form factor and potentially low cost and can find its own space of application.
E-compass technology is becoming used in platforms such as low-cost navigation devices including position sensing devices and portable including mobile communication devices with position sensing using positioning technologies such as satellite positioning (e.g., global positioning system GPS) and/or positioning based on transmissions from one or more cell base stations. Accelerometer technology is also becoming used in such devices. In this way, when the positioning technology may have some variation and accuracy or service availability, such as due to variations in GPS visibility, the e-compass can complement the positioning technology and the accelerometer can also complement the positioning technology.
Direction signals from an e-compass can suffer from inaccuracy due to tilt errors and from magnetic disturbances called Hard Iron error and Soft Iron error. The Soft Iron error happens when the e-compass is subjected to time varying magnetic fields. The hard iron effect is a constant magnetic field that creates an additional disturbance to the e-compass heading measurement.
An accelerometer can be used to estimate tilt of the device or platform in a given resting position, but such tilt estimation is itself subject to enough error so that the direction signals from an e-compass can still suffer from inaccuracy due to tilt errors. Thus, even if tilt compensation of an e-compass is attempted based on accelerometer data, residual errors due to inadequate tilt compensation may exist due to non-idealities of the accelerometers.
Mobile telephony can communicate video and digital data, and voice over packet (VoP or VoIP), in addition to cellular voice. Streams of information such as video, voice, audio content, images of all kinds, and data should be flexibly handled by such portable including mobile devices or platforms. But power dissipation can limit time between battery recharges and limit the features and number of applications running. And system latency might cause various kinds of delays and lapses in desirable application operation.
Processors of various types, including DSP (digital signal processing) chips, RISC (reduced instruction set computing), information storage memories and/or other integrated circuit blocks and devices are important to these systems and applications. Containing or reducing energy dissipation, system latency and the cost of manufacture while providing a variety of circuit, device and system products with performance features for different market segments are important goals in integrated circuits generally and system-on-a-chip (SOC) design.